// The MIT License (MIT)
//
// Copyright (c) 2012-2013 Mikola Lysenko
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

/**
 * SurfaceNets in JavaScript
 *
 * Written by Mikola Lysenko (C) 2012
 *
 * MIT License
 *
 * Based on: S.F. Gibson, "Constrained Elastic Surface Nets". (1998) MERL Tech Report.
 */

class SurfaceNets{
  constructor(){
    this.cube_edges = new Int32Array(24);
    this.edge_table = new Int32Array(256);
    
    var k = 0;
    for(var i=0; i<8; ++i) {
      for(var j=1; j<=4; j<<=1) {
        var p = i^j;
        if(i <= p) {
          this.cube_edges[k++] = i;
          this.cube_edges[k++] = p;
        }
      }
    }
    
      //Initialize the intersection table.
      //  This is a 2^(cube configuration) ->  2^(edge configuration) map
      //  There is one entry for each possible cube configuration, and the output is a 12-bit vector enumerating all edges crossing the 0-level.
    for(var i=0; i<256; ++i) {
      var em = 0;
      for(var j=0; j<24; j+=2) {
        var a = !!(i & (1<<this.cube_edges[j]))
          , b = !!(i & (1<<this.cube_edges[j+1]));
        em |= a !== b ? (1 << (j >> 1)) : 0;
      }
      this.edge_table[i] = em;
    }
  }
  
  createSurface(data, dims) {
    return new Promise( resolve =>{
      let buffer = new Int32Array(4096);
      var vertices = []
        , faces = []
        , n = 0
        , x = new Int32Array(3)
        , R = new Int32Array([1, (dims[0]+1), (dims[0]+1)*(dims[1]+1)])
        , grid = new Float32Array(8)
        , buf_no = 1;
        
      //Resize buffer if necessary 
      if(R[2] * 2 > buffer.length) {
        buffer = new Int32Array(R[2] * 2);
      }
      
      //March over the voxel grid
      for(x[2]=0; x[2]<dims[2]-1; ++x[2], n+=dims[0], buf_no ^= 1, R[2]=-R[2]) {
      
        //m is the pointer into the buffer we are going to use.  
        //This is slightly obtuse because javascript does not have good support for packed data structures, so we must use typed arrays :(
        //The contents of the buffer will be the indices of the vertices on the previous x/y slice of the volume
        var m = 1 + (dims[0]+1) * (1 + buf_no * (dims[1]+1));
        
        for(x[1]=0; x[1]<dims[1]-1; ++x[1], ++n, m+=2)
        for(x[0]=0; x[0]<dims[0]-1; ++x[0], ++n, ++m) {
        
          //Read in 8 field values around this vertex and store them in an array
          //Also calculate 8-bit mask, like in marching cubes, so we can speed up sign checks later
          var mask = 0, g = 0, idx = n;
          for(var k=0; k<2; ++k, idx += dims[0]*(dims[1]-2))
          for(var j=0; j<2; ++j, idx += dims[0]-2)      
          for(var i=0; i<2; ++i, ++g, ++idx) {
            var p = data[idx];
            grid[g] = p;
            mask |= (p < 0) ? (1<<g) : 0;
          }
          
          //Check for early termination if cell does not intersect boundary
          if(mask === 0 || mask === 0xff) {
            continue;
          }
          
          //Sum up edge intersections
          var edge_mask = this.edge_table[mask]
            , v = [0.0,0.0,0.0]
            , e_count = 0;
            
          //For every edge of the cube...
          for(var i=0; i<12; ++i) {
          
            //Use edge mask to check if it is crossed
            if(!(edge_mask & (1<<i))) {
              continue;
            }
            
            //If it did, increment number of edge crossings
            ++e_count;
            
            //Now find the point of intersection
            var e0 = this.cube_edges[ i<<1 ]       //Unpack vertices
              , e1 = this.cube_edges[(i<<1)+1]
              , g0 = grid[e0]                 //Unpack grid values
              , g1 = grid[e1]
              , t  = g0 - g1;                 //Compute point of intersection
            if(Math.abs(t) > 1e-6) {
              t = g0 / t;
            } else {
              continue;
            }
            
            //Interpolate vertices and add up intersections (this can be done without multiplying)
            for(var j=0, k=1; j<3; ++j, k<<=1) {
              var a = e0 & k
                , b = e1 & k;
              if(a !== b) {
                v[j] += a ? 1.0 - t : t;
              } else {
                v[j] += a ? 1.0 : 0;
              }
            }
          }
          
          //Now we just average the edge intersections and add them to coordinate
          var s = 1.0 / e_count;
          for(var i=0; i<3; ++i) {
            v[i] = x[i] + s * v[i];
          }
          
          //Add vertex to buffer, store pointer to vertex index in buffer
          buffer[m] = vertices.length;
          vertices.push(v);
          
          //Now we need to add faces together, to do this we just loop over 3 basis components
          for(var i=0; i<3; ++i) {
            //The first three entries of the edge_mask count the crossings along the edge
            if(!(edge_mask & (1<<i)) ) {
              continue;
            }
            
            // i = axes we are point along.  iu, iv = orthogonal axes
            var iu = (i+1)%3
              , iv = (i+2)%3;
              
            //If we are on a boundary, skip it
            if(x[iu] === 0 || x[iv] === 0) {
              continue;
            }
            
            //Otherwise, look up adjacent edges in buffer
            var du = R[iu]
              , dv = R[iv];
            
            //Remember to flip orientation depending on the sign of the corner.
            if(mask & 1) {
              faces.push([buffer[m], buffer[m-du], buffer[m-du-dv], buffer[m-dv]]);
            } else {
              faces.push([buffer[m], buffer[m-dv], buffer[m-du-dv], buffer[m-du]]);
            }
          }
        }
      }
        
        //All done!  Return the result
      resolve({ vertices: vertices, faces: faces });
    });
  }
}